Jelly-roll of improved productivity and battery cell comprising the same

ABSTRACT

Disclosed herein is a jelly roll for a secondary battery configured by winding a cathode sheet, a separator, and an anode sheet, wherein electrode tabs are connected to uncoated portions of the electrode sheets, to which electrode active materials are not applied, by welding, and each of the electrode tabs is configured to have an embossed structure protruding toward the uncoated portion to improve weldability.

TECHNICAL FIELD

The present invention relates to a jelly roll exhibiting improved productivity and a battery cell including the same, and, more particularly, to a jelly roll for a secondary battery configured by winding a cathode sheet, a separator, and an anode sheet, wherein electrode tabs are connected to uncoated portions of the electrode sheets, to which electrode active materials are not applied, by welding, and each of the electrode tabs is configured to have an embossed structure protruding toward the uncoated portion to improve weldability.

BACKGROUND ART

As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as mobile devices.

Based on the shape of a battery case, a secondary battery may be classified as a cylindrical battery having an electrode assembly mounted in a cylindrical metal container, a prismatic battery having an electrode assembly mounted in a prismatic metal container, or a pouch-shaped battery having an electrode assembly mounted in a pouch-shaped case formed of an aluminum laminate sheet. The cylindrical battery has advantages in that the cylindrical battery has relatively large capacity and is structurally stable.

The electrode assembly mounted in the battery case serves as a power generating element, having a cathode/separator/anode stack structure, which can be charged and discharged. The electrode assembly may be classified as a jelly roll type electrode assembly configured to have a structure in which a long sheet type cathode and a long sheet type anode, to which active materials are applied, are wound in a state in which a separator is disposed between the cathode and the anode, a stacked type electrode assembly configured to have a structure in which a plurality of cathodes having a predetermined size and a plurality of anodes having a predetermined size are sequentially stacked in a state in which separators are disposed respectively between the cathodes and the anodes, or a stacked/folded type electrode assembly, which is a combination of the a jelly roll type electrode assembly and the stacked type electrode assembly.

In this connection, the structure of a conventional cylindrical secondary battery is shown in FIG. 1.

Referring to FIG. 1, a cylindrical secondary battery 100 is manufactured by mounting a jelly roll type (wound type) electrode assembly 120 in a battery case 130, injecting an electrolyte into the battery case 130, and coupling a cap assembly 140 having an electrode terminal (for example, a cathode terminal, which is not shown) to the upper end, which is open, of the battery case 130.

The electrode assembly 120 is configured to have a structure in which a cathode sheet 121 and an anode sheet 122 are wound in a circle in a state in which a separator 123 is disposed between the cathode sheet 121 and the anode sheet 122. A cylindrical center pin 150 is fitted in the core of the electrode assembly 120 (the center of the jelly roll). The center pin 150 is generally made of a metal material to exhibit predetermined strength. The center pin 150 is configured to have a hollow cylindrical structure formed by rolling a sheet type material. The center pin 150 serves to fix and support the electrode assembly. Also, the center pin 150 serves as a passage to discharge gas generated by internal reaction of the secondary battery when charging and discharging the secondary battery and when operating the secondary battery.

An insulation member 160, which is configured to have a sheet type structure, is mounted at the upper end of the electrode assembly 120. The insulation member 160 is provided at the center thereof with an opening communicating with a through hole 151 of the center pin 150, through which gas can be discharged and through which a cathode tab 142 of the electrode assembly 120 can be connected to a cap plate 145 of the cap assembly 140.

Also, an insulation member 170 is disposed at the lower end of the cylindrical secondary battery 100. The insulation member 170 is located between the lower end of the electrode assembly 120 and the battery case 130. The insulation member 170 is provided at the center thereof with an opening, through which an anode tab (not shown) attached to the anode sheet 122 is connected to the lower end of the battery case 130.

The cathode tab and the anode tab are generally connected to uncoated portions of the cathode sheet and the anode sheet (portions of the electrode sheets, i.e. metal current collectors, to which electrode active materials are not applied) by ultrasonic welding.

Specifically, ultrasonic welding between the cathode sheet and the cathode tab is typically shown in a sectional view of FIG. 2.

Referring to FIG. 2, the cathode tab 142 is disposed on an uncoated portion 121 a of the cathode sheet in contact with the uncoated portion 121 a of the cathode sheet, and the cathode tab 142 is pressed by an ultrasonic welding device 300 including a plurality of horn tips 310. At this time, ultrasonic vibration is transmitted to the cathode tab 142, and the cathode tab 142 is welded to the uncoated portion 121 a of the cathode sheet by frictional heat generated as the result of the ultrasonic vibration.

However, the cathode tab and the cathode sheet are flat with the result that the cathode tab may wear down when ultrasonic welding is performed in a state in which the horn tips are in contact with the cathode tab. Also, high coupling between the cathode tab and the cathode sheet is required, and therefore, electrode active materials may be separated from the cathode sheet during welding based on the application of high ultrasonic waves.

Therefore, there is a high necessity for technology to fundamentally solve the above problems.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the above problems, and other technical problems that have yet to be resolved.

It is an object of the present invention to provide a jelly roll in which an embossed structure is formed at each electrode tab, preventing wear of the electrode tabs and improving weldability during ultrasonic welding.

It is another object of the present invention to provide a secondary battery using the jelly roll with improved productivity and safety.

Technical Solution

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a secondary battery configured by winding a cathode sheet, a separator, and an anode sheet, wherein electrode tabs are connected to uncoated portions of the electrode sheets, to which electrode active materials are not applied, by welding, and each of the electrode tabs is configured to have an embossed structure protruding toward the uncoated portion to improve weldability.

That is, the embossed structures as described above are formed at the jelly roll according to the present invention. When comparing with the conventional structure in which welding is performed with respect to flat electrode tabs, therefore, high friction between the electrode tabs (specifically, portions having the embossed structures) and the uncoated portions of the electrode sheets is achieved although a vibration energy level is lowered during welding, thereby improving weldability between the electrode tabs and the uncoated portions.

The electrode tabs may be made of aluminum or nickel. For example, the cathode tab may be made of aluminum, and the anode tab may be made of nickel; however, the present invention is not limited thereto.

In a preferred example, the embossed structure may include a plurality of micro protrusions configured to have a structure having protruding parts formed at one side thereof facing the uncoated portion and depressed parts formed at the other side thereof so as to correspond to the protrusions.

The shape of the protruding parts and the depressed parts is not particularly restricted. Preferably, the protruding parts and the depressed parts are formed in the shape of a hemisphere.

Preferably, each of the micro protrusions has a protruding height of 50 to 500 microns. If the protruding height is too high, welding between the electrode tabs and the uncoated portions is not easily achieved, which is not preferable. On the other hand, if the protruding height is too high, it is difficult for the embossed structures to function, which is not also preferable. More preferably, each of the micro protrusions has a protruding height of 100 to 150 microns.

Meanwhile, the electrode tabs are connected to the uncoated portions, preferably, by ultrasonic welding to minimize deformation of welded portions and to achieve easy application with respect to thin uncoated portions.

Concretely, the ultrasonic welding may be performed by a welding device comprising horn tips arranged at intervals corresponding to the micro protrusions of the embossed structure.

Consequently, welding is performed by the horn tips corresponding to the micro protrusions, thereby maximizing weldability between the electrode tabs and the uncoated portions.

Also, the ultrasonic welding may be performed by applying ultrasonic waves in a state in which the horn tips are located in the depressed parts of the respective micro protrusions.

In the conventional ultrasonic welding, it is necessary for the height of each of the horn tips contacting the electrode tabs to be about 350 microns so that vibration energy generated from the horn tips can be effectively transmitted to the corresponding surfaces of the electrode sheets contacting the electrode tabs. However, the horn tips, the height of which is relatively high, may be easily damaged. In addition, the electrode tabs may be worn by the horn tips.

According to the present invention, on the other hand, the protruding parts are formed at the regions of the electrode tabs corresponding to the depressed parts of the electrode tabs, in which the horn tips are located, i.e. the regions of the electrode tabs facing the uncoated portions, and therefore, it is possible to provide high weldability simply by reducing the height of each of the horn tips. Consequently, it is possible to solve problems, such as wear of the electrode tabs.

Concretely, each of the horn tips preferably has a height of 50 to 300 microns, more preferably about 100 microns.

Meanwhile, each of the horn tips 320 may have an angle of 60 to 120 degrees. Preferably, each of the horn tips is formed in the shape of a pyramid having an angle of 90 degrees.

In accordance with another aspect of the present invention, there is provided a method of manufacturing the jelly roll. Concretely, the method of manufacturing the jelly roll includes (a) winding a cathode sheet and an anode sheet in a state in which a separator is disposed between the cathode sheet and the anode sheet, (b) positioning electrode tabs each having an embossed structure formed at a surface thereof on uncoated portions of the cathode sheet and the anode sheet so that protruding parts of the embossed structure face a corresponding one of the uncoated portions, and (c) positioning horn tips of a welding device in depressed parts of the embossed structure of each of the electrode tabs and applying ultrasonic waves to the depressed parts.

That is, ultrasonic welding is performed using the horn tips corresponding to the embossed structure, thereby minimizing wear of the electrode tabs and improving weldability between the electrode tabs and the uncoated portions.

In accordance with another aspect of the present invention, there is provided a battery cell including the jelly roll, wherein the jelly roll is mounted in a battery case.

The battery cell is a secondary battery which can be continuously charged and discharged. The battery cell may be configured in various forms, such as a prismatic battery and a cylindrical battery cell. Preferably, the battery cell is a cylindrical battery cell.

Also, the battery cell is preferably applied to a middle or large-sized battery module of high power and large capacity comprising a plurality of battery cells as unit cells by virtue of excellent weldability.

The structure of the middle or large-sized battery module and a method of manufacturing the same are well known in the art to which the present invention pertains, and a detailed description thereof will be omitted.

Advantageous Effects

As is apparent from the above description, the jelly roll according to the present invention has the embossed structures protruding toward the uncoated portions. Consequently, it is possible to minimize wear of the electrode tabs and to improve weldability, thereby improving safety of the battery cell.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical sectional perspective view showing a conventional cylindrical secondary battery;

FIG. 2 is a partial sectional view showing welding between a cathode sheet and a cathode tab of FIG. 1;

FIG. 3 is a partial sectional view showing welding between a cathode sheet and a cathode tab according to an embodiment of the present invention;

FIG. 4 is a front view showing a welding device according to the present invention with a partial side view of the welding device; and

FIG. 5 is a photograph showing a portion of an electrode tab of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Now, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. It should be noted, however, that the scope of the present invention is not limited by the illustrated embodiment.

FIG. 3 is a partial sectional view showing welding between a cathode sheet and a cathode tab according to an embodiment of the present invention, FIG. 4 is a front view showing a welding device of FIG. 3 with a partial side view of the welding device, and FIG. 5 is a photograph showing a portion of an electrode tab of FIG. 3.

Referring to these drawings together with FIG. 1, a jelly roll 120 for a secondary battery is configured by winding a cathode sheet 121, a separator 123, and an anode sheet 122. A cathode tab 200, which is made of a nickel material, is connected to an uncoated portion 121 a of the cathode sheet 121, to which an electrode active material is not applied, by ultrasonic welding. The cathode tab 200 is configured to have an embossed structure which protrudes toward the uncoated portion 121 a to improve weldability.

The embossed structure includes a plurality of micro protrusions 210 configured to have a structure having protruding parts 212 formed at one side thereof facing the uncoated portion 121 a and depressed parts 214 formed at the other side thereof so as to correspond to the protrusions 212.

Each of the micro protrusions 210 has a protruding height H of about 120 microns.

Meanwhile, ultrasonic welding is performed by a welding device 300 including horn tips 320 arranged at intervals corresponding to the micro protrusions 210 of the embossed structure.

The welding device 300 includes horn tips 320 arranged in a 3×9 matrix. Each of the horn tips 320 has a height L of about 100 microns. Also, each of the horn tips 320 is formed in the shape of a pyramid having an angle R of 90 degrees.

Ultrasonic welding is performed by applying ultrasonic waves in a state in which the horn tips are located in the depressed parts 214 of the respective micro protrusions 210. Consequently, it is possible to minimize wear of the electrode tab even in a case in which horn tips 320, the height of each of which is low, are used.

Such ultrasonic welding may be performed with respect to an anode tab, which is made of an aluminum material, in the same manner.

Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

1. A jelly roll for a secondary battery configured by winding a cathode sheet, a separator, and an anode sheet, wherein electrode tabs are connected to uncoated portions of the electrode sheets, to which electrode active materials are not applied, by welding, and each of the electrode tabs is configured to have an embossed structure protruding toward the uncoated portion to improve weldability.
 2. The jelly roll according to claim 1, wherein the electrode tabs are made of aluminum or nickel.
 3. The jelly roll according to claim 1, wherein the embossed structure comprises a plurality of micro protrusions configured to have a structure having protruding parts formed at one side thereof facing the uncoated portion and depressed parts formed at the other side thereof so as to correspond to the protrusions.
 4. The jelly roll according to claim 3, wherein each of the micro protrusions has a protruding height of 50 to 500 microns.
 5. The jelly roll according to claim 3, wherein each of the micro protrusions has a protruding height of 100 to 150 microns.
 6. The jelly roll according to claim 1, wherein the electrode tabs are connected to the uncoated portions by ultrasonic welding.
 7. The jelly roll according to claim 6, wherein the ultrasonic welding is performed by a welding device comprising horn tips arranged at intervals corresponding to the micro protrusions of the embossed structure.
 8. The jelly roll according to claim 7, wherein the ultrasonic welding is performed by applying ultrasonic waves in a state in which the horn tips are located in the depressed parts of the respective micro protrusions.
 9. A method of manufacturing a jelly roll according to claim 1, the method comprising: (a) winding a cathode sheet and an anode sheet in a state in which a separator is disposed between the cathode sheet and the anode sheet; (b) positioning electrode tabs each having an embossed structure formed at a surface thereof on uncoated portions of the cathode sheet and the anode sheet so that protruding parts of the embossed structure face a corresponding one of the uncoated portions; and (c) positioning horn tips of a welding device in depressed parts of the embossed structure of each of the electrode tabs and applying ultrasonic waves to the depressed parts.
 10. A battery cell comprising a jelly roll according to claim 1, wherein the jelly roll is mounted in a battery case.
 11. The battery cell according to claim 10, wherein the battery cell is a cylindrical battery or a prismatic battery.
 12. A battery module comprising a plurality of battery cells according to claim 11 as unit cells. 